convert factorials to gamma-function format
adding factorial test case
be more explicit with the rewrite operation
stripping trailing whitespace
adding negative number test case
only rewrite for positive z0
use is_positive in favor of __ge__

relevant issue: http://code.google.com/p/sympy/issues/detail?id=2832
adding symbolic z0 test case for factorials
Travis: enable gmpy tests by default
Fixed domain conversions in Poly.eval() (#3245)

In [1]: var('alpha,l')
Out[1]: (α, l)

In [2]: A = Matrix([[-alpha*x**2 + x - y], [-alpha*y - x*y + x]])

In [3]: f = A.jacobian([x, y]).subs({x: 0, y: 0}).charpoly()

In [4]: f.eval((z + 1)/(z - 1))
Out[4]:
               2
2⋅α⋅z - 2⋅α + z  + 3
────────────────────
     2
    z  - 2⋅z + 1

In [5]: f.as_expr(l).subs(l, (z + 1)/(z - 1)).cancel()
Out[5]:
               2
2⋅α⋅z - 2⋅α + z  + 3
────────────────────
     2
    z  - 2⋅z + 1
Fix test_code_quality.py failure: trailing whitespace in polytools.py
Fix whitespace error introduced by #1812
Merge pull request #1807 from certik/travis_enable

Travis: enable gmpy tests by default
Merge pull request #1734 from perimosocordiae/master

Fix for #1733: mishandling of factorials when taking limits
Add CJ Carey to the AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #1815 from mattpap/issue_3245-poly-eval

Fixed domain conversions in Poly.eval() (#3245)
Merge branch 'master' into 3626